Doping induced magnetism in Co–ZnS nanoparticles

Zn1−xCoxS nanoparticles with x=0, 0.1, 0.2, and 0.3 were synthesized by the co-precipitation method using thiophenol as capping agent. The effect of Co doping on the structural, optical and magnetic properties are investigated. The X-ray diffraction patterns show single phase with cubic structure and the images of Transmission Electron Microscopy indicate an average particle size of 39 nm. Significant blue shift in the optical absorbing band edge was observed with increasing Co doping. In the Co doped samples, room-temperature (RT) magnetic hysteresis is observed and the magnetization reduces with increasing Co content. However, these samples show paramagnetic resonance instead of ferromagnetic resonance at both 300 and 80 K, suggesting that the origin of RT magnetization in these Zn1−xCoxS nanoparticles involves with the frustration of antiferromagnetic interactions.

Figure shows the magnetization data of Zn1−xCoxS (0.1≤x≤0.3) nanoparticles annealed at 573 K/2 h in vacuum and measured at 300 K. This interesting feature of systematic reduction in magnetization may be due to introduction of antiferromagnetic ordering with increasing ‘Co’ concentration which may be due to competition between the antiferromagnetic and ferromagnetic ordering within the sample. One could also observe the exchange bias effect which is an interface interaction observed in a ferromagnetic–antiferromagnetic mixture. The exchange bias field (loop shift) towards negative field was around 63 Oe for the Zn1−xCoxS (0.1≤x≤0.3) nanoparticles.Figure optionsDownload as PowerPoint slide